The present invention relates to a method and a plant for recovery of oil, spilled on a water surface.
In the event of a collision with or grounding of a tanker or an accident at an off-shore oil well the oil as a rule is spilled on the water surface. The tankers of today being enormous, the damage of an oil spill is devastating to beaches as well as to bird-life and fishing.
If a really big accident occurs, gathering and recovery of the oil spill is beyond the capacity of present technique. There is a certain readiness for minor accidents and spills but major accidents demand a technique yet unknown.
Oil spills on water have thus far often been fought by chemical means, in order to sink the oil into the sea and make it harmless. At a large cost the ocean surface is rendered free of oil slicks but instead the vegetation at the bottom is given a large addition of nutriment. This causes large changes in the ecological system.
In the event of major accidents, oil is spilled in large quantities representing a great economic value.
By mechanical recovery of oil spill today, booms are used to corral the oil slick and gather the oil to a layer of a thickness enough to enable mechanical collection from the water surface. The collection is performed either by suction or by means of skimmers.
UK patent specification No. 947 026 discloses a skimmer. This plant operates satisfactory but has too low an efficiency to be usable at big oil spills.
One of the problems which must be solved in collecting oil on a water surface is the fact that the oil is spread into a thin surface layer over a large area. In order to efficiently collect the oil, it is required that the oil layer is thickened. This is customary performed by means of oil booms arranged in the form of a V. The oil corralled by the booms is gathered at the apex of the V and the oil layer is thereby made thicker.
The collected mixture of oil and water is pumped by pumping means from the water surface to a separation vessel where the oil is settled or separated from the water. The water is given off to the surroundings.
U.S. Pat. No. 4,067,811 to Dallamore discloses an apparatus for separating floating pollutants, particularly oil, from a body of water. The appparatus comprises a vessel having an opening in its side to define an inlet for the mixture of the oil and the top water layer. There are means within the vessel to impart a whirlpool motion to the admitted mixture and a nozzle is positioned at about the center of the whirlpool means projecting upwardly. A separator is positioned beneath the nozzle and the oil is separated from the body of the water.
However, this apparatus is too sensitive to waves to be usable at the open sea. The inlet usually faces the waves and any wave entering the inlet will immediately disturb the whirlpool motion and move the whirlpool away from the nozzle.
U.S. Pat. No. 3,726,406 to Damberger discloses a skimmer body floating on the body of water by means of floatable members, the floatable members being of such a capacity as to support the skimmer body with the upper surface of the front floatable member underlying the oil to be collected. The oil slick is drawn to the oil skimmer body by a cable water fence. A vacuum pump removes the oil from the skimmer body into a separator and then to an oil tanker. A hot water spray head is arranged to heat the oil from beneath the same just immediately to its passing over the upper surface of the front floating body.
This device is also severely disturbed by wave motion.